1. Field of the Invention
The present invention relates to a piezoelectric resonator used for e.g., discriminators or trap filters, and more particularly, to an energy-trap type piezoelectric resonator utilizing the thickness shear vibration mode, and also relates to a method of manufacturing the same. The present invention further relates to a piezoelectric component including this piezoelectric resonator.
2. Description of the Related Art
In a conventional piezoelectric component such as a discriminator or a trap filter utilizing the thickness shear vibration mode, a piezoelectric resonator is mounted in the accommodating space of a case. The energy-trap type piezoelectric resonator utilizing the thickness shear vibration mode has vibration electrodes that are provided on portions of the two main surfaces of a piezoelectric substrate so as to be opposed to each other. In order to provide desired values for electrical characteristics such as resonance characteristics, group delay characteristics, or distortion factor in the piezoelectric resonator, a method for providing both main surfaces of the piezoelectric substrate with a damping member made of silicone rubber has been widely used. One example is disclosed in Japanese Unexamined Patent Application Publication No. 7-235853.
In the conventional piezoelectric resonator, however, since there is a need to provide both main surfaces of the piezoelectric substrate with a damping member, the processes of applying the damping member must be executed twice. This raises a problem that the number of the manufacturing steps for a piezoelectric resonator or a piezoelectric component using this piezoelectric resonator increases, thereby increasing the cost thereof.
In order to overcome the problems described above, preferred embodiments of the present invention provide a low-cost piezoelectric resonator which is easily producible and which has superior electrical characteristics, and further provide a method of manufacturing such a novel piezoelectric resonator, as well as a piezoelectric component including this piezoelectric resonator.
In accordance with a first preferred embodiment of the present invention, an energy-trap type piezoelectric resonator which utilizes the thickness shear mode includes a piezoelectric substrate, and at least a pair of vibration electrodes which are provided on portions of first and second main surfaces, respectively, of the piezoelectric substrate, which are arranged so as to be opposed to each other, and which constitute a vibrating portion. The piezoelectric resonator further includes a damping member which is arranged so as to cover the vibrating portion only on one main surface of the piezoelectric resonator and a pair of side surfaces connecting the first and second main surfaces thereof.
In the first preferred embodiment of the present invention, it is preferable that the damping member is made of silicone rubber which has a viscosity of about 20 Paxc2x7s or below at approximately 25xc2x0 C., which has fluidity at about 25xc2x0 C., and which is cured into a rubber-like state by heating. In this specification, the viscosity is a value measured in accordance with the method defined by JIS K6249.
In accordance with a second preferred embodiment of the present invention, a piezoelectric component includes a piezoelectric resonator in accordance with the first preferred embodiment of the present invention, and first and second case members which are bonded to each other, and in which an accommodating space for accommodating the piezoelectric resonator is provided. In this piezoelectric component, the piezoelectric resonator is fixed on one of the first and second case members so as not to hinder vibrations of the piezoelectric vibrating portion.
In accordance with a third preferred embodiment of the present invention, a method for manufacturing a piezoelectric resonator includes the steps of preparing an energy-trap type piezoelectric resonator which utilizes the thickness shear mode and in which the vibration electrodes are formed on the first and second main surfaces thereof, respectively, applying a damping member from one main surface side of the piezoelectric resonator and so as to coat the damping member on the vibrating portion only on one main surface and both side surfaces.
In the third preferred embodiment of the present invention, the step of applying of the damping member is preferably performed using a nozzle or a transfer pin.
Preferably, a nozzle or a transfer pin which satisfies the relationship Dxe2x89xa7W is used, when the widthwise dimension of the piezoelectric substrate is W, and the outer diameter of the nozzle or the diameter of the transfer pin is D, at the portion where the damping member droops from the tip of the nozzle or the transfer pin.
In the third preferred embodiment of the present invention, more preferably, the damping member is provided so as to satisfy the relationship 0xe2x89xa6Axe2x89xa6t, when the distance between the lower end of the portion where the damping member droops from the tip of the nozzle or the transfer pin and the main surface opposite to the main surface on the side where the damping member of the piezoelectric substrate is to be applied, is A, and the thickness of the piezoelectric substrate is t.
The above and other elements, characteristics, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.